[cros] Mobile activation - temporary whitelist disk I/O on UI thread.
[cros] Mobile activation - temporary whitelist disk I/O on UI thread.

BUG=chromium-os:11535
TEST=No DCHECKs during activation.

Review URL: http://codereview.chromium.org/6368078

git-svn-id: http://src.chromium.org/svn/trunk/src@73629 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 0423d0aaddf86aaf8542184d68e1c38df11ef995
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser